The persistent attempts by PG Wodehouse's friends to enable the author to return to Britain without fear of prosecution for alleged war crimes during the second world war are revealed in newly declassified documents at the National Archives.

The Jeeves and Wooster author recorded a series of broadcasts for the Nazis during the second world war while he was being held prisoner in Germany. Recorded in Berlin, they included his description of the German army as "a fine body of men, rather prettily dressed in green, carrying machine guns", and led to accusations of treason and to Wodehouse's investigation and interrogation by MI5. His embarrassment and distress over the affair meant the author never returned to the UK, moving to America instead where he continued to write.

The archive, a mix of letters and official documents, reveals the repeated pleas from friends and admirers for the government to lift the threat of prosecution from the ageing author's head. "He was nothing more than a silly ass!" wrote a friend of the broadcasts in 1947, while a letter the same year to the then Solicitor General Sir Frank Soskice from the biographer Hesketh Pearson begged: "Can you tell me … whether he may assume that should he return to England he would not be troubled by anything in the nature of, to borrow his own terminology, 'phonus-bolonus', oompus-boompus or runny gazoo?'"

Pearson believed that Wodehouse "should be told either that he can return without a trial or that he would have to face proceedings on his arrival" in order to "put an end to a state of suspense which in view of Mr Wodehouse's age and the great pleasure his works have given to thousands of his fellow countrymen has surely lasted long enough".

But his pleas fell on deaf ears. "I am bound to say that I have no sympathy with Mr Hesketh Pearson when he says in regard to a man who succeeded in procuring for himself an exceedingly comfortable war by doing for the Germans something which they, at all events, considered to be of assistance to them, that he ought not to be troubled by 'anything in the nature of 'phonus-bolonus'," wrote the attorney general Sir Hartley Shawcross, who felt that "strong public feeling would be aroused if Wodehouse were allowed to return and go free".

Wodehouse's case, wrote the director of public prosecutions in 1945, was "a very notorious one, and I think that there might be strong public feeling if he is allowed to come back to this country and to the advantages of British citizenship here without any action being taken about him."

As late as 1965, enquiries about whether Wodehouse would be prosecuted if he visited the UK to attend his grandson's wedding were met with the response that it was not possible "to give you an absolute assurance that in no circumstances would Mr PG Wodehouse be prosecuted if he were to come to this country".

"He had a capital charge against his name. This haunted him for most of his life and never went away. While he was privately exonerated in 1944, this was never publicised, so he was sort of left in limbo for the rest of his life which was a very cruel thing to do," said Robert McCrum, Wodehouse's biographer and associate editor of the Observer. "He made a very ill-judged set of actions, which he'd be the first to admit, but he became a lightning conductor for wartime paranoia. He got caught up in a hysterical response."

The papers show that even Wodehouse's literary agent, AP Watt, was considered for prosecution under the 1939 Trading with the Enemy Act for planning publication of Wodehouse's new manuscript, Money in the Bank. "As Wodehouse was regarded as an enemy under the Trading with the Enemy Act, 1939, publication was prohibited by that Act, and their possession of the manuscript should be reported to the Custodian [of Enemy Property for England]", the Attorney-General was told by a solicitor in July 1942. "The Ministry of Information … expressed the view that publication of a new novel after Wodehouse's notorious broadcasts last autumn from Berlin was highly undesirable."

McCrum said this was not surprising. "They would have been liable as his agents," he said. "It was part of the hysterical atmosphere at the time."